Evaluation of rotating slant-hole SPECT mammography using Monte Carlo simulation methods

Multisegment slant-hole (MSSH) collimators provide much higher detection efficiency at a single view as compared to conventional low-energy high-resolution (LEHR) parallel-hole collimators with the same spatial resolution. The purpose of this study is to evaluate rotating MSSH (RMSSH) SPECT mammography using Monte Carlo simulation methods. We modified the SIMIND Monte Carlo code to generate RMSSH projection data including the effects of attenuation, collimator-detector response and scatter from a realistic 4-D NCAT phantom with attached breasts and lesions placed in the central, medial, and lateral regions of the breast. The projection data were reconstructed using analytic and iterative image reconstruction methods. For comparison, we examine planar scintimammography images obtained by placing an LEHR collimator with a resolution of 1 cm at 15.2 cm, which is the same as that of a four-segment slant-hole (4SSH) collimator at the center of its common volume-of-view, in close proximity to the lateral wall of the breast. Also, we simulated the inclusion of a lead shield that covers the body to keep photons emitted from the other organs from reaching the MSSH collimator. Our results indicated that, depending on the lesion location, the spatial resolution of the RMSSH SPECT images may be comparable or slightly poorer than that of the planar scintimammographic images obtained using a LEHR collimator while the lesion contrast is significantly higher at all lesion locations. Shielding of photon emissions from the other organs substantially improves the RMSSH SPECT image quality. We conclude that the Monte Carlo simulation methods are useful in evaluating the application of RMSSH SPECT to breast imaging as compared to conventional planar scintimammography and that RMSSH SPECT provides higher overall image quality.